Envelope trackers providing compensation for power amplifier output load variation

ABSTRACT

Envelope trackers providing compensation for power amplifier output load variation are provided herein. In certain configurations, a radio frequency (RF) system includes an antenna, a power amplifier that receives a radio frequency signal and outputs an amplified radio frequency signal to the antenna, a plurality of detectors coupled to the power amplifier and operable to generate a plurality of detection signals, and an envelope tracker that controls a supply voltage of the power amplifier based on an envelope of the radio frequency signal. The envelope tracker processes the plurality of detection signals to generate a load variation detection signal indicating a change in an output load of the power amplifier arising from a change in a voltage standing wave ratio (VSWR) of the antenna. Additionally, the envelope tracker adjusts a gain of the power amplifier based on the load variation detection signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/969,075, filed May 2, 2018, titled “ENVELOPE TRACKERS PROVIDINGCOMPENSATION FOR POWER AMPLIFIER OUTPUT LOAD VARIATION,” which claimsthe benefit of priority under 35 U.S.C. § 119 of U.S. Provisional PatentApplication No. 62/505,275, filed May 12, 2017 and titled “ENVELOPETRACKERS PROVIDING COMPENSATION FOR POWER AMPLIFIER OUTPUT LOADVARIATION,” each of which is herein incorporated by reference in itsentirety.

BACKGROUND Field

Embodiments of the invention relate to electronic systems, and inparticular, to power amplifiers for radio frequency (RF) electronics.

Description of the Related Technology

Power amplifiers are used in radio frequency (RF) systems to amplify RFsignals for transmission via antennas. It is important to manage thepower of RF signal transmissions to prolong battery life and/or toprovide a suitable transmit power level.

Examples of RF systems with one or more power amplifiers include, butare not limited to, mobile phones, tablets, base stations, networkaccess points, customer-premises equipment (CPE), laptops, and wearableelectronics. For example, in wireless devices that communicate using acellular standard, a wireless local area network (WLAN) standard, and/orany other suitable communication standard, a power amplifier can be usedfor RF signal amplification. An RF signal can have a frequency in therange of about 30 kilohertz (kHz) to 300 gigahertz (GHz), such as in therange of about 450 megahertz (MHz) to about 6 GHz for certaincommunications standards.

SUMMARY

In certain embodiments, the present disclosure relates to a radiofrequency system. The radio frequency system includes a power amplifierincluding an input configured to receive a radio frequency signal and anoutput configured to provide an amplified radio frequency signal. Thepower amplifier is configured to receive power from a power amplifiersupply voltage. The radio frequency system further includes an outputdetector coupled to the output of the power amplifier and configured togenerate an output detection signal, an input detector coupled to theinput of the power amplifier and configured to generate an inputdetection signal, and an envelope tracker configured to generate thepower amplifier supply voltage based on an envelope of the radiofrequency signal and to compensate the power amplifier for output loadvariation based on the output detection signal and the input detectionsignal.

In various embodiments, at least one of the input detector or the outputdetector includes a peak detector.

In a number of embodiments, at least one of the input detector or theoutput detector includes an average detector.

In several embodiments, at least one of the input detector or the outputdetector includes a directional coupler.

In some embodiments, at least one of the input detector or the outputdetector includes a voltage detector.

In various embodiments, the output detection signal indicates a standingwave voltage at the output of the power amplifier.

In some embodiments, the output detection signal indicates a voltagegain at the output of the power amplifier, the envelope trackerconfigured to provide compensation for output load variation based oncomparing the voltage gain to a target gain.

In a number of embodiments, the output detection signal indicates both avoltage gain and a forward gain at the output of the power amplifier,and the envelope tracker is configured to provide compensation foroutput load variation based on comparing the voltage gain to the forwardgain.

In several embodiments, the output detection signal indicates both aforward wave and a reverse wave at the output of the power amplifier.

In various embodiments, the input detection signal indicates an inputpower level of the power amplifier.

In some embodiments, the envelope tracker includes a load variationdetector configured to generate a load variation detection signal basedon compensating an output load variation indicated by the outputdetection signal by a nominal output load variation indicated by theinput detection signal. According to several embodiments, the envelopetracker is configured to adjust at least one of a voltage level of thepower amplifier supply voltage or a gain of the power amplifier based onthe load variation detection signal. In accordance with a number ofembodiments, the envelope tracker includes an envelope modulatorconfigured to generate the power amplifier supply voltage based on ashaped envelope signal, and an envelope adjustment circuit configured togenerate the shaped envelope signal based on shaping the envelope of theradio frequency signal. According to various embodiments, the envelopeadjustment circuit includes a shaping table, and the envelope adjustmentcircuit is configured to select a gain adjustment value of the shapingtable based on the load variation detection signal. In accordance withseveral embodiments, the envelope modulator includes a DC-to-DCconverter and an amplifier configured to operate in combination with oneanother to generate the power amplifier supply voltage.

In a number of embodiments, the radio frequency system further includesa duplexing and switching circuit coupled to the output of the poweramplifier, the output detector configured to provide output detectionprior to the duplexing and switching circuit.

In certain embodiments, the present disclosure relates to a mobiledevice. The mobile device includes a transceiver configured to generatea radio frequency signal, a front end system, and a power managementsystem including an envelope tracker. The front end system includes apower amplifier configured to provide amplification to the radiofrequency signal, an output detector configured to generate an outputdetection signal indicating an output signal condition of the poweramplifier, and an input detector configured to generate an inputdetection signal indicating an input signal condition of the poweramplifier. The envelope tracker is configured to generate a poweramplifier supply voltage of the power amplifier based on an envelope ofthe radio frequency signal, and the envelope tracker is furtherconfigured to compensate the power amplifier for output load variationbased on the output detection signal and the input detection signal.

In a number of embodiments, the mobile device further includes anantenna configured to receive an amplified radio frequency signal fromthe power amplifier, and the envelope tracker is configured tocompensate the power amplifier for output load variation arising from avoltage standing wave ratio condition of the antenna.

In several embodiments, at least one of the input detector or the outputdetector includes a peak detector.

In some embodiments, at least one of the input detector or the outputdetector includes an average detector.

In various embodiments, at least one of the input detector or the outputdetector includes a directional coupler.

In a number of embodiments, at least one of the input detector or theoutput detector includes a voltage detector.

In various embodiments, the output detection signal indicates a standingwave voltage at the output of the power amplifier.

In several embodiments, the output detection signal indicates both avoltage gain and a forward gain of the power amplifier, and the envelopetracker is configured to provide compensation for output load variationbased on comparing the voltage gain to the forward gain.

In a number of embodiments, the output detection signal indicates both aforward wave and a reverse wave at an output of the power amplifier.

In some embodiments, the output detection signal indicates a voltagegain of the power amplifier, and the envelope tracker is configured toprovide compensation for output load variation based on comparing thevoltage gain to a target gain.

In various embodiments, the output detection signal indicates both avoltage gain and a forward gain of the power amplifier, and the envelopetracker is configured to provide compensation for output load variationbased on comparing the voltage gain to the forward gain.

In several embodiments, the input detection signal indicates an inputpower level of the power amplifier.

In some embodiments, the envelope tracker includes a load variationdetector configured to generate a load variation detection signal basedon compensating an output load variation indicated by the outputdetection signal by a nominal output load variation indicated by theinput detection signal. According to various embodiments, the envelopetracker is configured to adjust at least one of a voltage level of thepower amplifier supply voltage or a gain of the power amplifier based onthe load variation detection signal. In accordance with a number ofembodiments, the envelope tracker includes an envelope modulatorconfigured to generate the power amplifier supply voltage based on ashaped envelope signal, and an envelope adjustment circuit configured togenerate the shaped envelope signal based on shaping the envelope of theradio frequency signal. According to several embodiments, the envelopeadjustment circuit includes a shaping table, and the envelope adjustmentcircuit is configured to select a gain adjustment value of the shapingtable based on the load variation detection signal. In accordance withvarious embodiments, the envelope modulator includes a DC-to-DCconverter and an amplifier configured to operate in combination with oneanother to generate the power amplifier supply voltage.

In certain embodiments, the present disclosure relates to a method ofenvelope tracking in a radio frequency system. The method includesamplifying a radio frequency signal using a power amplifier, generatingan output detection signal indicating an output signal condition of thepower amplifier using an output detector of the power amplifier,generating an input detection signal indicating an input signalcondition of the power amplifier using an input detector of the poweramplifier, generating a power amplifier supply voltage for the poweramplifier based on an envelope of the radio frequency signal using anenvelope tracker, and compensating the power amplifier for output loadvariation based on the output detection signal and the input detectionsignal using the envelope tracker.

In a number of embodiments, the method further includes compensating thepower amplifier for output load variation arising from a voltagestanding wave ratio condition of an antenna.

In some embodiments, generating the input detection signal includesperforming at least one of peak detection or average detection.

In several embodiments, generating the output detection signal includesperforming at least one of peak detection or average detection.

In a number of embodiments, the method further includes determining astanding wave voltage at an output of the power amplifier. According toseveral embodiments, the method further includes determining a voltagegain of the power amplifier, and providing compensation for output loadvariation based on comparing the voltage gain to a target gain.

In some embodiments, the method further includes determining a voltagegain and a forward gain of the power amplifier, and providingcompensation for output load variation based on comparing the voltagegain to the forward gain.

In various embodiments, the method further includes, determining aforward wave and a reverse wave at an output of the power amplifier.

In several embodiments, the method further includes generating a loadvariation detection signal based on compensating an output loadvariation indicated by the output detection signal by a nominal outputload variation indicated by the input detection signal, and providingcompensation for output load variation based on the load variationdetection signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of a transmission systemfor transmitting radio frequency (RF) signals.

FIG. 2A is a schematic diagram of an RF system including an envelopetracker according to one embodiment.

FIG. 2B is a schematic diagram of an RF system including an envelopetracker according to another embodiment.

FIG. 2C is a schematic diagram of an RF system including an envelopetracker according to another embodiment.

FIG. 2D is a schematic diagram of an RF system including an envelopetracker according to another embodiment.

FIG. 3A is schematic diagram of an RF system according to anotherembodiment.

FIG. 3B is schematic diagram of an RF system according to anotherembodiment.

FIG. 3C is schematic diagram of an RF system according to anotherembodiment.

FIG. 3D is schematic diagram of an RF system according to anotherembodiment.

FIG. 4A is a graph of one example of voltage versus phase angle for astanding wave.

FIG. 4B is one example of a graph of current versus voltage for a poweramplifier.

FIG. 5A is a graph showing a first example of power amplifier supplyvoltage versus time.

FIG. 5B is a graph showing a second example of power amplifier supplyvoltage versus time.

FIG. 6 is a schematic diagram of one embodiment of a communicationsystem.

FIG. 7A is a schematic diagram of one embodiment of a packaged module.

FIG. 7B is a schematic diagram of a cross-section of the packaged moduleof FIG. 7A taken along the lines 7B-7B.

FIG. 8 is a schematic diagram of one embodiment of a phone board.

FIG. 9 is a schematic diagram of one embodiment of a mobile device.

DETAILED DESCRIPTION OF EMBODIMENTS

The following detailed description of certain embodiments presentsvarious descriptions of specific embodiments. However, the innovationsdescribed herein can be embodied in a multitude of different ways, forexample, as defined and covered by the claims. In this description,reference is made to the drawings where like reference numerals canindicate identical or functionally similar elements. It will beunderstood that elements illustrated in the figures are not necessarilydrawn to scale. Moreover, it will be understood that certain embodimentscan include more elements than illustrated in a drawing and/or a subsetof the elements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Power added efficiency (PAE) is one metric for rating a power amplifier,and can correspond to the ratio of the difference between the output andinput signal power to the DC power consumed by the power amplifier.

Envelope tracking is a technique that can be used to increase PAE of apower amplifier system by efficiently controlling a voltage level of apower amplifier supply voltage in relation to an envelope of the RFsignal amplified by the power amplifier. Thus, when the envelope of theRF signal increases, the voltage supplied to the power amplifier can beincreased. Likewise, when the envelope of the RF signal decreases, thevoltage supplied to the power amplifier can be decreased to reduce powerconsumption.

To maintain linearity when using envelope tracking, an envelope trackingsystem can use a shaping table that maps or converts an envelope signalto a shaped envelope signal. For example, an isogain shaping table iscalibrated to provide mapping between envelope signal levels andcorresponding shaped envelope signal levels while maintaining asubstantially constant gain across an envelope signal range. Using anisogain shaping table in an envelope tracking system can provide highlinearity over the range of the signal's envelope, thereby helping toensure that the power amplifier is compliant with a particularcommunications standard.

A variation in voltage standing wave ratio (VSWR) at an antenna can leadto a change in standing wave ratio at the output of the power amplifier.Thus, variation in VSWR can cause changes in the load of the poweramplifier, which in turn can lead to a change in the gain of the poweramplifier. For example, the power amplifier's gain can increase ordecrease in response to variation in load line impedance.

Output load variation can lead to the power amplifier operating awayfrom a desired gain and efficiency trajectory, thereby leading todegradation in signaling and/or power performance. For instance, inenvelope tracking systems that operate with an isogain shaping table,variations in output load can result in the power amplifier operatingunder higher or lower compression than desired.

Envelope trackers providing compensation for power amplifier output loadvariation are provided herein. In certain configurations, an RF systemincludes a power amplifier that amplifies an RF signal, an outputdetector coupled to an output of the power amplifier and that generatesan output detection signal, an input detector coupled to an input of thepower amplifier and that generates an input detection signal, and anenvelope tracker that generates a power amplifier supply voltage for thepower amplifier based on an envelope of the RF signal. The envelopetracker compensates the power amplifier for output load variation basedon the output detection signal and the input detection signal.

For example, the envelope tracker can include a load variation detectorthat generates a load variation detection signal based on determining anoutput load variation indicated by the output detection signal ascompensated for by a nominal variation in output load indicated by theinput detection signal. For instance, a change in input power level ofthe RF signal can lead to a nominal output load variation. By correctingfor nominal output load variation, a component of output load variationcorresponding to the power amplifier's standing wave ratio can bedetected.

Thus, the envelope tracker can provide compensation for variation in thepower amplifier's load line impedance arising from changes in VSWR.

The output load variation can be detected using detectors implemented ina wide variety of ways.

In a first example, the output detector detects the standing wavevoltage at the power amplifier's output. For instance, the outputdetector can be implemented as a peak detector.

In a second example, the output detector generates the output detectionsignal to indicate a voltage gain of the power amplifier, which can becompared to a target gain. For instance, the output detector can beimplemented as an average detector.

In a third example, the output detector measures both the voltage gainand the forward gain at the output of the power amplifier, which can becompared to one another. For instance, the output detector can includean average detector for measuring voltage gain and a directional couplerfor measuring forward gain.

In a fourth example, the output detector measures a forward wave and areverse wave at the power amplifier's output. For instance, the outputdetector can include a directional coupler for measuring a forward waveand a reverse wave at the output of the power amplifier.

In certain implementations, the envelope tracker provides compensationfor output load variation based on adjusting at least one of a voltagelevel of the power amplifier supply voltage or a gain of the poweramplifier based on the load variation detection signal.

In one example, the envelope tracker includes a shaping table (forinstance, an isogain shaping table) for mapping between envelope signallevels and corresponding shaped envelope signal levels. Additionally,the selected shaped envelope signal level is chosen in part based on theload variation detection signal.

In another example, the envelope tracker processes the load variationdetection signal to control a value of a gain control signal of thepower amplifier.

The teachings herein can be used to detect an output load condition asVSWR changes. Additionally, the envelope tracker provides compensationfor output load variation to maintain the power amplifier in a region ofhigh efficiency and linearity. For instance, the envelope tracker canlower a voltage at the power amplifier's output when output loadimpedance is relatively low and increase the voltage at the poweramplifier's output when output load impedance is relatively high. Thecompensation is provided dynamically during operation of the mobilephone or other communication device.

FIG. 1 is a schematic diagram of one example of a transmission system 50for transmitting RF signals. The transmission system 50 includes abattery 21, an antenna 22, an envelope modulator 30, a power amplifierbiasing circuit 31, a power amplifier 32, a duplexing and switchingcircuit 33, a baseband processor 34, a signal delay circuit 35, an I/Qmodulator 37, a coordinate rotation digital computation (CORDIC) circuit40, and an envelope adjustment circuit 41. In the illustratedembodiment, the envelope adjustment circuit 41 includes a shapingcircuit 42, a delay circuit 43, a digital-to-analog converter 44, and areconstruction filter 45.

The baseband processor 34 can be used to generate an I signal and a Qsignal, which correspond to signal components of a sinusoidal wave orsignal of a desired amplitude, frequency, and phase. For example, the Isignal can be used to represent an in-phase component of the sinusoidalwave and the Q signal can be used to represent a quadrature component ofthe sinusoidal wave, which can be an equivalent representation of thesinusoidal wave. In certain implementations, the I and Q signals can beprovided to the I/Q modulator 37 in a digital format. The basebandprocessor 34 can be any suitable processor configured to process abaseband signal. For instance, the baseband processor 34 can include adigital signal processor, a microprocessor, a programmable core, or anycombination thereof.

The delay circuit 35 provides adjustable delay to the I and Q signals toaid in controlling relative alignment between the shaped envelope signaland the RF signal RFin.

The I/Q modulator 37 can be configured to receive the I and Q signalsfrom the baseband processor 34 and to process the I and Q signals togenerate an RF signal RFin. For example, the I/Q modulator 37 caninclude DACs configured to convert the I and Q signals into an analogformat, mixers for upconverting the I and Q signals to radio frequency,and a signal combiner for combining the upconverted I and Q signals intoan RF signal suitable for amplification by the power amplifier 32. Incertain implementations, the I/Q modulator 37 can include one or morefilters configured to filter frequency content of signals processedtherein.

In the illustrated embodiment, the CORDIC circuit 40 processes the I andQ signals to generate an envelope signal corresponding to an envelope ofthe RF signal RFin. Although FIG. 1 illustrates an implementation usinga CORDIC circuit to generate an envelope signal, an envelope signal canbe obtained in other ways.

The envelope adjustment circuit 41 includes the shaping circuit 42,which is used to shape the envelope signal to enhance the performance ofthe transmission system 50. In certain implementations, the shapingcircuit 42 includes a shaping table that maps each level of the envelopesignal to a corresponding shaped envelope signal level. The delaycircuit 43 provides adjustable delay to aid in controlling relativealignment between the shaped envelope signal and the RF signal RFin. Inthe illustrated embodiment, the delayed envelope signal generated by thedelay circuit 43 is a digital signal, which is converted by the DAC 44to an analog envelope signal. Additionally, the analog envelope signalis low pass filtered by the reconstruction filter 45 to generate ashaped envelope signal suitable for use by the envelope modulator 30.

The envelope modulator 30 can receive the shaped envelope signal fromthe envelope adjustment circuit 41 and a battery voltage V_(BATT) fromthe battery 21, and can use the shaped envelope signal to generate apower amplifier supply voltage V_(CC) _(_) _(PA) for the power amplifier32 that changes in relation to the envelope of the RF signal RFin. Thepower amplifier 32 can receive the RF signal RFin from the I/Q modulator37 of the transceiver 33, and can provide an amplified RF signal RFoutto the antenna 22 through the duplexing and switching circuit 33, inthis embodiment.

Although illustrated as a single stage, the power amplifier 32 caninclude one or more stages. Furthermore, the teachings herein areapplicable to power amplifier systems including multiple poweramplifiers.

FIG. 2A is a schematic diagram of an RF system 100 including an envelopetracker 102 according to one embodiment. The RF system 100 furtherincludes a power amplifier system 101 including a power amplifier thatamplifies an RF signal RFin to generate an amplified RF signal RFout.

The envelope tracker 102 of FIG. 2A illustrates one embodiment of anenvelope tracker that provides compensation to a power amplifier foroutput load variation. However, the teachings herein are applicable toenvelope trackers implemented in a wide variety of ways. Accordingly,other implementations are possible.

As shown in FIG. 2A, the envelope tracker 102 receives an envelopesignal corresponding to an envelope of the RF signal RFin. Additionally,the envelope tracker 102 generates a power amplifier supply voltageV_(CC) _(_) _(PA), which supplies power to the power amplifier system101.

The illustrated envelope tracker 102 includes an envelope modulatorimplemented using a DC-to-DC converter 111 and a high bandwidthamplifier 112 that operate in combination with one another to generatethe power amplifier supply voltage V_(CC) _(_) _(PA) based on theenvelope signal. The combination of the DC-to-DC converter 111 and thehigh bandwidth amplifier 112 can provide envelope tracking of widebandwidth envelope signals, since the DC-to-DC converter 111 can providesuperior tracking of low frequency components of the envelope signalwhile the high bandwidth amplifier 112 can provide superior tracking ofhigh frequency components of the envelope signal. In the illustratedembodiment, an output of the DC-to-DC converter 111 and an output of thehigh bandwidth amplifier 112 are combined using a combiner 115.

The high bandwidth amplifier 112 can be implemented in a variety ofways, such as using a linear amplifier or a relatively fast digitalamplifier. Although an embodiment using a high bandwidth amplifier isshown, other types of amplification circuits can be used.

As shown in FIG. 2A, the envelope tracker 102 further includes anenvelope adjustment circuit 110 that provides adjustment to the envelopesignal, such as envelope shaping. The envelope adjustment circuit 110also controls the DC-to-DC converter 111 and the high bandwidthamplifier 112. The envelope tracker 102 also includes a load variationdetector 116 used to generate a load variation detection signal based onan output detection signal and an input detection signal from the poweramplifier system 101.

The envelope tracker 102 compensates the power amplifier system 101 foroutput load variation based on the output detection signal and the inputdetection signal. In particular, the load variation detector 116generates the load variation detection signal based on determining anoutput load variation indicated by the output detection signal ascompensated for by a nominal variation in output load indicated by theinput detection signal. By correcting for nominal output load variation,a component of output load variation corresponding to the poweramplifier's standing wave ratio can be detected.

Thus, the envelope tracker 102 can provide compensation for variation inthe power amplifier's load line impedance arising from changes in VSWR.

The power amplifier system 101 can include detectors implemented in awide variety of ways. For example, the power amplifier system 101 caninclude peak detectors, average detectors, directional couplers, and/ora wide variety of other detector types for generating the outputdetection signal and/or input detection signal.

In certain implementations, the envelope tracker 102 providescompensation for output load variation based on adjusting a voltagelevel of the power amplifier supply voltage V_(CC) _(_) _(PA) based onthe load variation detection signal.

In one example, the envelope adjustment circuit 110 includes a shapingtable for mapping between envelope signal levels and correspondingshaped envelope signal levels. Additionally, the selected shapedenvelope signal level is chosen in part based on the load variationdetection signal.

In another example, the envelope adjustment circuit 110 provides gainadjustment to the power amplifier system 101 based on the load variationdetection signal.

Thus, the envelope tracker 102 detects the power amplifier system'soutput load condition as VSWR changes. Additionally, the envelopetracker 102 provides compensation for output load variation to maintainthe power amplifier system 101 operating in a region of high efficiencyand linearity.

The illustrated RF system 100 advantageously provides correction foroutput load variation without needing to receive indicators from atransceiver or RFIC. Implementing the RF system 100 in this mannerprovides enhanced flexibility and/or independence at the system levelfrom other components of a mobile device or other communication device.

FIG. 2B is a schematic diagram of an RF system 130 including an envelopetracker 122 according to another embodiment. The RF system 130 of FIG.2B is similar to the RF system 100 of FIG. 2A, except that the envelopetracker 122 includes an envelope adjustment circuit 125 including anisogain shaping table 126.

The isogain shaping table 126 can be calibrated to providing mappingbetween envelope signal levels and corresponding shaped envelope signallevels while maintaining a substantially constant gain across anenvelope signal range. Configuring the envelope tracker 122 in thismanner can provide high linearity over the range of the signal'senvelope, thereby helping to ensure that the power amplifier iscompliant with a particular communications standard.

In the illustrated embodiment, the selected shaped envelope signal levelfrom the isogain shaping table 126 is chosen in part based on the loadvariation detection signal from the load variation detector 116.Accordingly, in this embodiment the power amplifier system 101 iscompensated for output load variation arising from changes to VSWR basedon the value selected from the isogain shaping table 126.

FIG. 2C is a schematic diagram of an RF system 140 including an envelopetracker 132 according to another embodiment. The RF system 140 of FIG.2C is similar to the RF system 100 of FIG. 2A, except that the envelopetracker 132 includes an envelope adjustment circuit 135 including a gainleveling circuit 136. The gain leveling circuit 136 provides levelingcontrol to maintain a power amplifier gain substantially constant acrossan envelope signal range.

In the illustrated embodiment, an adjustment to the gain levelingcircuit 136 (for instance, a correction to an amount of gain levelingprovided) is made based on the load variation detection signal tothereby provide compensation for output load variation.

FIG. 2D is a schematic diagram of an RF system 150 including an envelopetracker 142 according to another embodiment. The RF system 150 of FIG.2D is similar to the RF system 100 of FIG. 2A, except that the envelopetracker 142 includes an envelope adjustment circuit 145 including a gaincontrol circuit 146.

In the illustrated embodiment, the gain control circuit 146 providesgain adjustment to the power amplifier system 101 based on the loadvariation detection signal from the load variation detector 116.Accordingly, in this embodiment the envelope tracker 142 provides gainadjustment to the power amplifier system 101 to compensate for outputload variation arising from changes to VSWR.

The gain control circuit 146 can provide gain adjustment to the poweramplifier system 101 in a variety of ways. For example, the gain of thepower amplifier system 101 can be adjusted by controlling a bias of atransistor (for instance a base bias of a bipolar transistor and/or agate bias of a field-effect transistor). Additionally, althoughillustrated in the context of a single gain adjustment signal, theenvelope tracker 142 can provide gain adjustment in a variety of ways,such as by using multiple gain adjustment signals to control the gain ofone or more power amplifier stages.

FIG. 3A is schematic diagram of an RF system 170 according to anotherembodiment. The RF system 170 includes an antenna 22, a duplexing andswitching circuit 33, a power amplifier 151, an envelope tracker 152, abias controller 153, an input detector 154, and an output detector 155.

The power amplifier 151 provides amplification to a radio frequencysignal RFin, and provides an amplified radio frequency signal RFout tothe antenna 22 via the duplexing and switching circuit 33. In theillustrated embodiment, the power amplifier 151 includes a first stage157 and a second stage 158, which are in a cascade. Thus, the poweramplifier 151 is a multi-stage power amplifier, in this embodiment.

The bias controller 153 generates a first bias signal BIAS1 for thefirst stage 157 of the power amplifier 151, and a second bias signalBIAS2 for the second stage 158 of the power amplifier 151. The firstbias signal BIAS1 and the second bias signal BIAS2 can include a biascurrent, a bias voltage, or a combination thereof. In certainconfigurations, the bias controller 153 is implemented using amanufacturing technology suitable for fabricating metal oxidesemiconductor (MOS) transistors, such as a complementary metal oxidesemiconductor (CMOS) process.

The illustrated envelope tracker 152 includes a DC-to-DC converter 161,an amplifier 162, a load variation detection circuit 163, an envelopeadjustment circuit 164, and a combiner 165. In the illustratedembodiment, an output of the DC-to-DC converter 161 and an output of theamplifier 162 are combined using the combiner 165.

As shown in FIG. 3A, the power amplifier supply voltage V_(CC) _(_)_(PA) is controlled based on an output of the DC-to-DC converter 161 andon an output of the amplifier 162. The envelope adjustment circuit 164receives an envelope signal, and processes the envelope signal togenerate a shaped envelope signal and control signals suitable forcontrolling the DC-to-DC converter 161 and the amplifier 162.

In the illustrated embodiment, the RF system 170 communicates withexternal circuitry (for instance, a transceiver or RFIC) via a serialinterface, such as a Mobile Industry Processor Interface (MIPI) radiofrequency front end (RFFE) bus. For example, the serial interface can beused to control bias settings of the bias controller 153 and/or toprovide data to the envelope tracker 152, such as data identifyingoperating mode, operating band, and/or characteristics of the radiofrequency signal RFin.

The input detector 154 is coupled to an input of the power amplifier 151and generates an input detection signal. Additionally, the outputdetector 155 is coupled to an output of the power amplifier 151 andgenerates an output detection signal. The envelope tracker 152 generatesthe power amplifier supply voltage V_(CC) _(_) _(PA) for the poweramplifier 151 based on the envelope signal. Additionally, the envelopetracker 152 compensates the power amplifier 151 for output loadvariation based on the output detection signal and the input detectionsignal.

For example, the load variation detector 163 processes the outputdetection signal and the input detection signal to generate a loadvariation detection signal corresponding to an output load variationindicated by the output detection signal as compensated for by a nominalvariation in output load indicated by the input detection signal.Additionally, the envelope tracker 152 uses the load variation detectionsignal to compensate for output load variation corresponding to thepower amplifier's standing wave ratio.

Accordingly, the envelope tracker 152 provides compensation forvariation in the power amplifier's load line impedance arising fromchanges in VSWR of the antenna 22.

The output load detector 155 can be implemented in a wide variety ofways.

In a first example, the output detector 155 detects the standing wavevoltage at the power amplifier's output. For instance, the outputdetector 155 can be implemented as a peak detector.

In a second example, the output detector 155 generates the outputdetection signal to indicate a voltage gain of the power amplifier 151,which can be compared to a target gain using the envelope tracker 152.For instance, the output detector 155 can be implemented as an averagedetector.

In a third example, the output detector 155 measures both the voltagegain and the forward gain at the output of the power amplifier 151,which can be compared to one another. For instance, the output detector155 can include an average detector for measuring voltage gain and adirectional coupler for measuring forward gain.

In a fourth example, the output detector 155 measures a forward wave anda reverse wave at the power amplifier's output. For instance, the outputdetector 155 can include a directional coupler for measuring a forwardwave and a reverse wave at the output of the power amplifier 151.

As shown in FIG. 3A, the output detector 155 provides output detectionat the output of the power amplifier 151 prior to the duplexing andswitching circuit 33. Implementing output detection in this mannerprovides output detection of higher accuracy. For instance, the outputdetection signal does not include insertion loss associated with theduplexing and switching circuit 33.

The input detector 154 can be implemented in a wide variety of ways,including, but not limited to, using a peak detector, an averagedetector, a directional coupler, or a combination thereof. In certainimplementations, the input detector 154 is operable to detect an inputpower level of the RF input signal RFin.

In certain implementations, the envelope tracker 152 providescompensation for output load variation based on adjusting at least oneof a voltage level of the power amplifier supply voltage V_(CC) _(_)_(PA) or a gain of the power amplifier 151 based on the load variationdetection signal.

The envelope tracker 152 can detect an output load condition as VSWRchanges. Additionally, the envelope tracker 152 provides compensationfor output load variation to maintain the power amplifier 151 in aregion of high efficiency and linearity. For instance, the envelopetracker 152 can lower a voltage at the power amplifier's output whenoutput load impedance is relatively low, and increase the voltage at thepower amplifier's output when output load impedance is relatively high.The compensation is provided dynamically during operation of the mobilephone or other communication device that includes the RF system 170.

FIG. 3B is schematic diagram of an RF system 190 according to anotherembodiment. The RF system 190 of FIG. 3B is similar to the RF system 170of FIG. 3A, except that the RF system 190 illustrates a specificimplementation of an input detector implemented as an input voltagedetector 174 and of an output detector implemented as an output voltagedetector 175. Additionally, the RF system 190 includes an envelopetracker 182 that controls an amount of gain of the power amplifier 151.

The input voltage detector 174 and the output voltage detector 175 canbe implemented in a wide variety of ways, such as using peak detectorsand/or average detectors.

In one example, a detector can include a diode and a capacitor of a sizesuitable for detecting a peak of an RF signal.

In another example, a detector can include a diode and a capacitor of asize suitable for detecting an average of an RF signal.

In yet another example, a detector can include a non-linear amplifier(for instance, a log amp) implemented to detect a peak and/or an averageof an RF signal.

Although various examples of detectors have been described, input andoutput detectors can be implemented in a wide variety of ways.

FIG. 3C is schematic diagram of an RF system 195 according to anotherembodiment. The RF system 195 of FIG. 3C is similar to the RF system 190of FIG. 3B, except that the RF system 195 illustrates an implementationwith an output detector implemented as a directional coupler 191.

The directional coupler 191 can be used to measure a forward wave at theoutput of the power amplifier 151, a reverse wave at the output of thepower amplifier 151, or both the forward wave and the reverse wave atthe output of the power amplifier 151.

FIG. 3D is schematic diagram of an RF system 200 according to anotherembodiment. The RF system 200 of FIG. 3D is similar to the RF system 190of FIG. 3B, except that the RF system 200 illustrates an implementationwith an output detector implemented as both an output voltage detector175 and a directional coupler 191.

Output load variation of a power amplifier can be detected usingdetectors implemented in a wide variety of ways.

In a first example, an output detector detects the standing wave voltageat the power amplifier's output. For instance, the output detector canbe implemented as a peak detector.

In a second example, the output detector generates the output detectionsignal to indicate a voltage gain of the power amplifier, which can becompared to a target gain. For instance, the output detector can beimplemented as an average detector.

In a third example, the output detector measures both the voltage gainand the forward gain at the output of the power amplifier, which can becompared to one another. For instance, the output detector can includean average detector for measuring voltage gain and a directional couplerfor measuring forward gain.

In a fourth example, the output detector measures a forward wave and areverse wave at the power amplifier's output. For instance, the outputdetector can include a directional coupler for measuring a forward waveand a reverse wave at the output of the power amplifier.

FIG. 4A is a graph of one example of voltage versus phase angle for astanding wave. When the standing wave is present at a power amplifier'soutput, the power amplifier's load line changes with the phase angle ofthe standing wave. For example, as shown in FIG. 4A, the load line ofthe power amplifier at angle A is different from the load line at angleB.

Since variation in a VSWR condition of an antenna can lead to a changein the standing wave ratio at the output of power amplifier, changes inVSWR can lead to load line changes.

FIG. 4B is one example of a graph of current versus voltage for a poweramplifier. The graph depicts that a load line presented to a poweramplifier changes based on power amplifier bias.

Although FIGS. 4A-4B illustrate various graphs of power amplifierperformance characteristics, a power amplifier can be implemented in avariety of ways, such as in a manner suited for a particular applicationand/or communication standard. Accordingly, the graphs are included forillustrative purposes only, and other simulation and/or measurementresults are possible.

FIG. 5A is a graph 217 showing a first example of power amplifier supplyvoltage versus time. The graph 217 illustrates the voltage of an RFsignal 211, the RF signal's envelope 212, and a power amplifier supplyvoltage 213 versus time. The graph 217 corresponds to one example ofwaveforms for an implementation in which the power amplifier supplyvoltage 213 is substantially fixed.

It can be important that the power amplifier supply voltage 213 of apower amplifier has a voltage greater than that of the RF signal 211.For example, powering a power amplifier using a power amplifier supplyvoltage that has a magnitude less than that of the RF signal can clipthe RF signal, thereby creating signal distortion and/or other problems.Thus, it can be important the power amplifier supply voltage 213 begreater than that of the envelope 212. However, it can be desirable toreduce a difference in voltage between the power amplifier supplyvoltage 213 and the envelope 212 of the RF signal 211, as the areabetween the power amplifier supply voltage 213 and the envelope 212 canrepresent lost energy, which can reduce battery life and increase heatgenerated in a wireless device.

FIG. 5B is a graph 218 showing a second example of power amplifiersupply voltage versus time. The graph 218 illustrates the voltage of anRF signal 211, the RF signal's envelope 212, and a power amplifiersupply voltage 214 versus time. The graph 218 corresponds to one exampleof waveforms for an implementation in which the power amplifier supplyvoltage 214 is generated by envelope tracking.

Envelope tracking is a technique that can be used to increase poweradded efficiency (PAE) of a power amplifier system by efficientlycontrolling a voltage level of a power amplifier supply voltage inrelation to an envelope of the RF signal amplified by the poweramplifier. Thus, when the envelope of the RF signal increases, thevoltage supplied to the power amplifier can be increased. Likewise, whenthe envelope of the RF signal decreases, the voltage supplied to thepower amplifier can be decreased to reduce power consumption.

In contrast to the power amplifier supply voltage 213 of FIG. 5A, thepower amplifier supply voltage 214 of FIG. 5B changes in relation to theenvelope 212 of the RF signal 211. The area between the power amplifiersupply voltage 214 and the envelope 212 in FIG. 5B is less than the areabetween the power amplifier supply voltage 213 and the envelope 212 inFIG. 5A, and thus the graph 218 of FIG. 5B can be associated with apower amplifier system having greater energy efficiency.

FIG. 6 is a schematic diagram of one embodiment of a communicationsystem 260 including a MIPI RFFE bus 251. The communication system 260further includes a transceiver 241, a power amplifier module 242, atransmit filter module 243, a receive filter module 244, a low noiseamplifier (LNA) module 245, an antenna switch module 246, a couplermodule 247, a sensor module 248, a power management module 249, and anantenna 250.

As shown in FIG. 6, various components of the communication system 260are interconnected by the MIPI RFFE bus 251. Additionally, thetransceiver 241 includes a master device of the MIPI RFFE bus 251, andeach of the RF components includes a slave device of the MIPI RFFE bus251. The master device of the transceiver 241 sends control commandsover the MIPI RFFE bus 251 to configure the communication system 260during initialization and/or while operational.

The power amplifier module 242 can include one or more power amplifiers.As shown in FIG. 6, the power amplifier module 242 receives one or morepower amplifier supply voltages from the power management module 249.The power management module 249 can include an envelope tracker thatgenerates at least one power amplifier supply voltage, and that isimplemented in accordance with the teachings herein.

Although FIG. 6 illustrates one example of a communication systemincluding a power management module and a power amplifier module, theteachings herein are applicable to communication systems implemented ina wide variety of ways.

FIG. 7A is a schematic diagram of one embodiment of a packaged module300. FIG. 7B is a schematic diagram of a cross-section of the packagedmodule 300 of FIG. 7A taken along the lines 7B-7B. The packaged module300 illustrates an example of a module that can include circuitryimplemented in accordance with one or more features of the presentdisclosure.

The packaged module 300 includes a first die 301, a second die 302,surface mount components 303, wirebonds 308, a package substrate 320,and encapsulation structure 340. The package substrate 320 includes pads306 formed from conductors disposed therein. Additionally, the dies 301,302 include pads 304, and the wirebonds 308 have been used to connectthe pads 304 of the dies 301, 302 to the pads 306 of the packagesubstrate 320.

In certain implementations, the dies 301, 302 are manufactured usingdifferent processing technologies. In one example, the first die 301 ismanufactured using a compound semiconductor process, and the second die302 is manufactured using a silicon process. Although an example withtwo dies is shown, a packaged module can include more or fewer dies.

The packaging substrate 320 can be configured to receive a plurality ofcomponents such as the dies 301, 302 and the surface mount components303, which can include, for example, surface mount capacitors and/orinductors.

As shown in FIG. 7B, the packaged module 300 is shown to include aplurality of contact pads 332 disposed on the side of the packagedmodule 300 opposite the side used to mount the dies 301, 302.Configuring the packaged module 300 in this manner can aid in connectingthe packaged module 300 to a circuit board such as a phone board of awireless device. The example contact pads 332 can be configured toprovide RF signals, bias signals, ground, and/or supply voltage(s) tothe dies 301, 302 and/or the surface mount components 303. As shown inFIG. 7B, the electrically connections between the contact pads 332 andthe die 301 can be facilitated by connections 333 through the packagesubstrate 320. The connections 333 can represent electrical paths formedthrough the package substrate 320, such as connections associated withvias and conductors of a multilayer laminated package substrate.

In some embodiments, the packaged module 300 can also include one ormore packaging structures to, for example, provide protection and/orfacilitate handling of the packaged module 300. Such a packagingstructure can include overmold or encapsulation structure 340 formedover the packaging substrate 320 and the components and die(s) disposedthereon.

It will be understood that although the packaged module 300 is describedin the context of electrical connections based on wirebonds, one or morefeatures of the present disclosure can also be implemented in otherpackaging configurations, including, for example, flip-chipconfigurations.

FIG. 8 is a schematic diagram of one embodiment of a phone board 350.The phone board 350 includes an envelope tracking module 352 and a poweramplifier module 351 attached thereto. In certain configurations, thepower amplifier module 351 and/or the envelope tracking module 352 areimplemented using one or more instantiations of the module 300 shown inFIGS. 7A-7B. As shown in FIG. 8, the envelope tracking module 352provides a power amplifier supply voltage V_(CC) _(_) _(PA) to the poweramplifier module 351. Additionally, the envelope tracking module 352controls the power amplifier supply voltage V_(CC) _(_) _(PA) to changein relation to the envelope of an RF signal amplified by the poweramplifier module 351.

Although not illustrated in FIG. 8 for clarity, the phone board 350includes additional components and structures.

FIG. 9 is a schematic diagram of one example of a mobile device 800. Themobile device 800 includes a baseband system 801, a transceiver 802, afront end system 803, antennas 804, a power management system 805, amemory 806, a user interface 807, and a battery 808.

The mobile device 800 can be used communicate using a wide variety ofcommunications technologies, including, but not limited to, 2G, 3G, 4G(including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G, WLAN (forinstance, Wi-Fi), WPAN (for instance, Bluetooth and ZigBee), WMAN (forinstance, WiMax), and/or GPS technologies.

The transceiver 802 generates RF signals for transmission and processesincoming RF signals received from the antennas 804. It will beunderstood that various functionalities associated with the transmissionand receiving of RF signals can be achieved by one or more componentsthat are collectively represented in FIG. 9 as the transceiver 802. Inone example, separate components (for instance, separate circuits ordies) can be provided for handling certain types of RF signals.

The front end system 803 aids is conditioning signals transmitted toand/or received from the antennas 804. In the illustrated embodiment,the front end system 803 includes power amplifiers (PAs) 811, low noiseamplifiers (LNAs) 812, filters 813, switches 814, and duplexers 815.However, other implementations are possible.

For example, the front end system 803 can provide a number offunctionalizes, including, but not limited to, amplifying signals fortransmission, amplifying received signals, filtering signals, switchingbetween different bands, switching between different power modes,switching between transmission and receiving modes, duplexing ofsignals, multiplexing of signals (for instance, diplexing ortriplexing), or some combination thereof.

In certain implementations, the mobile device 800 supports carrieraggregation, thereby providing flexibility to increase peak data rates.Carrier aggregation can be used for both Frequency Division Duplexing(FDD) and Time Division Duplexing (TDD), and may be used to aggregate aplurality of carriers or channels. Carrier aggregation includescontiguous aggregation, in which contiguous carriers within the sameoperating frequency band are aggregated. Carrier aggregation can also benon-contiguous, and can include carriers separated in frequency within acommon band or in different bands.

The antennas 804 can include antennas used for a wide variety of typesof communications. For example, the antennas 804 can include antennasassociated transmitting and/or receiving signals associated with a widevariety of frequencies and communications standards.

In certain implementations, the antennas 804 support MIMO communicationsand/or switched diversity communications. For example, MIMOcommunications use multiple antennas for communicating multiple datastreams over a single radio frequency channel. MIMO communicationsbenefit from higher signal to noise ratio, improved coding, and/orreduced signal interference due to spatial multiplexing differences ofthe radio environment. Switched diversity refers to communications inwhich a particular antenna is selected for operation at a particulartime. For example, a switch can be used to select a particular antennafrom a group of antennas based on a variety of factors, such as anobserved bit error rate and/or a signal strength indicator.

The mobile device 800 can operate with beamforming in certainimplementations. For example, the front end system 803 can include phaseshifters having variable phase controlled by the transceiver 802.Additionally, the phase shifters are controlled to provide beamformation and directivity for transmission and/or reception of signalsusing the antennas 804. For example, in the context of signaltransmission, the phases of the transmit signals provided to theantennas 804 are controlled such that radiated signals from the antennas804 combine using constructive and destructive interference to generatean aggregate transmit signal exhibiting beam-like qualities with moresignal strength propagating in a given direction. In the context ofsignal reception, the phases are controlled such that more signal energyis received when the signal is arriving to the antennas 804 from aparticular direction. In certain implementations, the antennas 804include one or more arrays of antenna elements to enhance beamforming.

The baseband system 801 is coupled to the user interface 807 tofacilitate processing of various user input and output (I/O), such asvoice and data. The baseband system 801 provides the transceiver 802with digital representations of transmit signals, which the transceiver802 processes to generate RF signals for transmission. The basebandsystem 801 also processes digital representations of received signalsprovided by the transceiver 802. As shown in FIG. 9, the baseband system801 is coupled to the memory 806 of facilitate operation of the mobiledevice 800.

The memory 806 can be used for a wide variety of purposes, such asstoring data and/or instructions to facilitate the operation of themobile device 800 and/or to provide storage of user information.

The power management system 805 provides a number of power managementfunctions of the mobile device 800. The power management system 805 caninclude an envelope tracker implemented in accordance with one or morefeatures of the present disclosure. For example, the envelope trackercan compensate one or more of the power amplifiers 811 for output loadvariation, such as changes to load line impedance arising from variationin a VSWR condition of the antennas 804.

As shown in FIG. 9, the power management system 805 receives a batteryvoltage form the battery 808. The battery 808 can be any suitablebattery for use in the mobile device 800, including, for example, alithium-ion battery.

CONCLUSION

Some of the embodiments described above have provided examples inconnection with mobile phones. However, the principles and advantages ofthe embodiments can be used for any other systems or apparatus that haveneeds for power amplifier systems.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Likewise, the word “connected”, as generally used herein, refers to twoor more elements that may be either directly connected, or connected byway of one or more intermediate elements. Additionally, the words“herein,” “above,” “below,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A radio frequency system comprising: an antenna;a power amplifier including an input configured to receive a radiofrequency signal and an output configured to provide an amplified radiofrequency signal to the antenna; a plurality of detectors coupled to thepower amplifier and configured to generate a plurality of detectionsignals; and an envelope tracker configured to control a supply voltageof the power amplifier based on an envelope of the radio frequencysignal, and to process the plurality of detection signals to generate aload variation detection signal indicating a change in an output load ofthe power amplifier arising from a change in a voltage standing waveratio of the antenna, the envelope tracker further configured to adjusta gain of the power amplifier based on the load variation detectionsignal.
 2. The radio frequency system of claim 1 wherein the envelopetracker is further configured to adjust a voltage level of the supplyvoltage of the power amplifier based on the load variation detectionsignal.
 3. The radio frequency system of claim 1 wherein the envelopetracker includes an envelope modulator configured to control the supplyvoltage of the power amplifier based on a shaped envelope signal, and anenvelope adjustment circuit configured to generate the shaped envelopesignal based on shaping the envelope of the radio frequency signal. 4.The radio frequency system of claim 3 wherein the envelope adjustmentcircuit includes a shaping table, the envelope adjustment circuitconfigured to select a gain adjustment value of the shaping table basedon the load variation detection signal.
 5. The radio frequency system ofclaim 1 wherein the plurality of detection signals includes an inputdetection signal and an output detection signal, the envelope trackerfurther configured to generate the load variation detection signal basedon compensating an output load variation indicated by the outputdetection signal by a nominal output load variation indicated by theinput detection signal.
 6. The radio frequency system of claim 1 whereinthe plurality of detectors include an input voltage detector coupled tothe input of the power amplifier, and an output voltage detector coupledto the output of the power amplifier.
 7. The radio frequency system ofclaim 6 wherein the plurality of detectors further include a directionalcoupler coupled to the output of the power amplifier.
 8. The radiofrequency system of claim 1 wherein the plurality of detectors includean input voltage detector coupled to the input of the power amplifier,and a directional coupler coupled to the output of the power amplifier.9. A method of envelope tracking in a mobile device, the methodcomprising: amplifying a radio frequency signal using a power amplifierto generate an amplified radio frequency signal for an antenna;generating a plurality of detection signals using a plurality ofdetectors coupled to the power amplifier; controlling a supply voltageof the power amplifier based on an envelope of the radio frequencysignal using an envelope tracker; and compensating the power amplifierfor output load variation using the envelope tracker, includingprocessing the plurality of detection signals to generate a loadvariation detection signal indicating a change in an output load of thepower amplifier arising from a change in a voltage standing wave ratioof the antenna, and adjusting a gain of the power amplifier based on theload variation detection signal.
 10. The method of claim 9 whereincompensating the power amplifier for output load variation using theenvelope tracker further includes adjusting a voltage level of thesupply voltage of the power amplifier based on the load variationdetection signal.
 11. The method of claim 9 wherein compensating thepower amplifier for output load variation using the envelope trackerfurther includes selecting a gain adjustment value of a shaping tablebased on the load variation detection signal.
 12. The method of claim 9wherein the plurality of detection signals includes an input detectionsignal and an output detection signal, the method further comprisinggenerating the load variation detection signal based on compensating anoutput load variation indicated by the output detection signal by anominal output load variation indicated by the input detection signal.13. A mobile device comprising: a front end system including a poweramplifier configured to amplify a radio frequency signal to generate anamplified radio frequency signal, and a plurality of detectors coupledto the power amplifier and configured to generate a plurality ofdetection signals; an antenna configured to transmit the amplified radiofrequency signal; and a power management system including an envelopetracker configured to control a supply voltage of the power amplifierbased on an envelope of the radio frequency signal, and to process theplurality of detection signals to generate a load variation detectionsignal indicating a change in an output load of the power amplifierarising from a change in a voltage standing wave ratio of the antenna,the envelope tracker further configured to adjust a gain of the poweramplifier based on the load variation detection signal.
 14. The mobiledevice of claim 13 further comprising a transceiver configured togenerate the radio frequency signal.
 15. The mobile device of claim 13wherein the envelope tracker is further configured to adjust a voltagelevel of the supply voltage of the power amplifier based on the loadvariation detection signal.
 16. The mobile device of claim 13 whereinthe envelope tracker includes a shaping table, the envelope trackerfurther configured to select a gain adjustment value of the shapingtable based on the load variation detection signal.
 17. The mobiledevice of claim 13 wherein the plurality of detection signals includesan input detection signal and an output detection signal, the envelopetracker further configured to generate the load variation detectionsignal based on compensating an output load variation indicated by theoutput detection signal by a nominal output load variation indicated bythe input detection signal.
 18. The mobile device of claim 13 whereinthe plurality of detectors include an input voltage detector coupled toan input of the power amplifier, and an output voltage detector coupledto an output of the power amplifier.
 19. The mobile device of claim 18wherein the plurality of detectors further include a directional couplercoupled to the output of the power amplifier.
 20. The mobile device ofclaim 13 wherein the plurality of detectors include an input voltagedetector coupled to an input of the power amplifier, and a directionalcoupler coupled to an output of the power amplifier.